Beckett, E. R. | bioRxiv Science

bioRxiv2026

Functional mapping of synaptotagmin 1 Ca2+ ligands that mediate excitation-secretion coupling in neurons

Synaptotagmin (SYT) 1 is a Ca2+ sensor that triggers rapid synaptic vesicle exocytosis, but how it is activated by Ca2+ remains enigmatic. SYT1 contains two Ca2+-sensing motifs, C2A and C2B. Structural studies have proposed that five acidic residues in each C2 domain mediate Ca2+-binding, but their functional relevance remains unclear. Here, we mutated each of the ten putative ligands and conducted side-by-side comparisons of Ca2+-binding activity and evoked glutamate release. Remarkably, all ten putative ligands are crucial for evoked synchronous release, overturning the view that binding of Ca2+ to C2A is dispensable. Importantly, Ca2+ binding to C2B is essential for synchronization. Furthermore, we report that two new human mutations, corresponding to Ca2+ ligands in C2B, are dominant-negative. Finally, four new crystal structures reveal how the choice of neutralizing substitution differentially alters SYT1 structure and, consequently, function.

neuroscience↗

bioRxiv2025

Protein-Like Polymer for Inhibition of Tau Fibril Propagation in Human-Derived Models of Neurodegeneration

The misfolding, aggregation, and spread of tau protein fibrils underlie tauopathies, a diverse class of neurodegenerative diseases for which effective treatments remain elusive. Among these are corticobasal dementia (CBD) and progressive supranuclear palsy (PSP), canonical examples of 4-repeat (4R) tauopathies characterized by tau isoforms exclusively with four microtubule-binding repeat domains. We target this 4R tau isoform-specific mechanism by focusing on misfolded taus distinctive stem-loop-stem structural motif formed by the junction of the 4R-defining alternatively spliced exon and the adjacent constitutive exon. A synthetic peptide based on this stem-loop-stem sequence can induce aggregation and spread in an isoform-specific manner. Here, we develop a protein-like polymer (PLP) in which multiple copies of this synthetic peptide form a brush-like structure capable of preventing tau aggregation by binding and capping fibril ends in vitro, in human brain organoids, and in cellular models with an EC50 of 105 {+/-} 14 nM. PLPs demonstrate robust activity against fibrils derived from CBD and PSP patient brains and a PS19 mouse tauopathy model. Previous tau-targeted treatments have primarily focused on broad tau clearance, aggregation inhibition, or microtubule stabilization, often lacking isoform specificity and precision. In contrast, this approach targets the 4R tau isoforms unique structural motif, offering a tailored therapeutic intervention for diseases like CBD and PSP. Supported by prior studies showing blood-brain barrier penetrance and safety profiles, this tau-binding PLP offers a promising translational path toward clinical applications in tauopathy treatment.

neuroscience↗